As per my understanding - They differ in how their organisations are structured. Alma is mostly backed and supported by CloudLinux Inc, for whom, CentOS formed

As per my understanding - They differ in how their organisations are structured. Alma is mostly backed and supported by CloudLinux Inc, for whom, CentOS formed the basis of their commercial software. Rocky is a more grassroots affair - founded by some of the original CentOS founders. I’ve not used either distribution yet, so I cannot comment on how their documentation and community differ.